Eddy‐driven sources and sinks of nutrients in the upper ocean: Results from a 0.1° resolution model of the North Atlantic

Abstract

[1] A nitrate-based model of new production is incorporated into eddy-resolving (0.1°) simulations of the North Atlantic. The biological model consists of light and nutrient limited production within the euphotic zone and relaxation of the nitrate field to climatology below. Sensitivity of the solutions to the parameters of the biological model is assessed in a series of simulations. Model skill is quantitatively evaluated with observations using an objective error metric; simulated new production falls within the range of observed values at several sites throughout the basin. Results from the ''best fit'' model are diagnosed in detail. Mean and eddying components of the nutrient fluxes are separated via Reynolds decomposition. In the subtropical gyre, eddy-driven vertical advection of nutrients is sufficient to overcome the mean wind-driven downwelling in the region and fuels a significant fraction of the annual new production in that area. In contrast, eddies constitute a net sink of nutrients in the subpolar gyre. Geostrophic adjustment to deep winter convection through mesoscale processes causes a net flux of nutrients out of the euphotic zone; the magnitude of this sink is sufficient to counterbalance the mean wind-driven upwelling of nutrients over much of the region. On the basis of these simulations it appears that the oceanic mesoscale has major impacts on nutrient supply to, and removal from, the euphotic zone. INDEX TERMS: 4255

Physical controls and interannual variability of the Labrador Sea spring phytoplankton bloom in distinct regions

“…While previous model studies showed that eddies actually decrease nutrient availability in the Labrador Sea (McGillicuddy et al, 2003), which should adversely affect a bloom, our results are contrary. A third explanation for our results and those of McGillicuddy et al (2003) could be that eddies in this region do not supply additional nutrients, but rather aid in the haline stratification of the region, since these eddies tend to be fresh at the surface (Frajka-Williams et al, 2009).…”

“…A third explanation for our results and those of McGillicuddy et al (2003) could be that eddies in this region do not supply additional nutrients, but rather aid in the haline stratification of the region, since these eddies tend to be fresh at the surface (Frajka-Williams et al, 2009).…”

“…Besides wintertime mixing, recent studies have shown the importance of mesoscale eddies to nutrient supply in the subtropical gyre (McGillicuddy et al, 1998;Siegel et al, 1999;McGillicuddy et al, 2007). However, the same eddy effects were shown to have an opposite effect in the Labrador Sea (McGillicuddy et al, 2003).…”

Ocean surface currents from satellite data

“…Heat and salt transports can be calculated using currents, sea surface temperature (SST), and sea surface salinity. Ocean eddies are an important source of upwelling, a process that brings nutrient-rich deep waters to the surface to supply the food chain [McGillicuddy et al, 2003].…”

Mechanisms of northern North Atlantic biomass variability

“…At the same time, there is evidence that horizontal physical processes could play a role, particularly in the northern subtropical gyre or "intergyre" region of the North Atlantic [Williams and Follows, 1998;Dutkiewicz et al 2001;Follows and Dutkiewicz 2002;Oschlies 2002;McGillicuddy et al 2003;.…”